1. Field Of The Invention
The present invention relates to the cultivation and harvest of aquatic crustaceans of the families Cambaridae and Astacidae and more particularly, relates to a method and apparatus for the "baitless" harvesting of crawfish. This method and apparatus even more particularly relates to the harvest of crawfish through the use of cylindrical (not necessarily round), shaped hides (tubes), for the purpose of attracting crawfish; directional movement and confinement of crawfish through the additional use of sinking and/or floating trap door(s); and for the accumulation of crawfish by use of a collection chamber.
2. General Background
Within the growing aquaculture industry are two families and various species of eatable freshwater crustacea of which belong to the general Procambarus and Pacifastacus.
As an established, renewable industry in Louisiana and rapidly expanding to other states as well as foreign countries, crawfish farming provides a source of food which in the Southern United States is usually referred to as "crawfish", "crayfish" or "crawdads". Due to the popularity of crawfish in France and as a result of the "Acadian" or "Cajun" influence in Louisiana, the French term "ecrevisse" also denotes this animal.
Crawfish are consumed in large quantities during a typical crawfish season. Along the Gulf Coast, many seafood restaurants feature crawfish as a speciality preparing them in a variety of ways. In areas where crawfish are raised in abundance, large processing plants handle thousands of pounds of crawfish daily. Louisiana alone produces up to 70 million dollars worth of crawfish annually and has expanded acreage for crawfish culture every year since 1960 (2,000 acres) to 1985 (125,000 acres), with anticipated growth in the coming years expected to reach an excess of 400,000 acres.
The expansion of crawfish markets and production has brought into sharp focus some significant problems facing this industry. One of the major problems which each crawfish farmer must address is finding an economic and reliable means of harvesting a crop of crawfish. In many cases, the cost of harvesting crawfish approaches 50% of their market value. The use of bait as an attractant in conjunction with some sort of net or trap has been and remains the primary method for harvesting crawfish.
The simple method of catching crawfish with a piece of bait tied to a string is often used by children along roadside ditches. Recreational crawfishing by adults most frequently employees baited lift nets. The vast majority of the commercial crawfish catch is harvested using baited wire mesh traps having funnels. Such traps allow crawfish to easily enter attracted by the bait, but makes it difficult for them to find their way out of the trap.
In order for crawfish ponds to be considered productive, intensive and continuous harvesting must take place so as to remove crawfish as soon as they become market size and thereby making the limited space and food supply available to be used by smaller and immature crawfish. Current recommendations call for daily harvest using thirty to forty traps per acre in commercial crawfish ponds. "Fishing" crawfish ponds in this manner produces for a maximum yield yet cost for buying storing and handling bait becomes critical. It is not uncommon for a 100 acre crawfish farm to incur expenses relating to bait to be in excess of $20,000 dollars during a single season.
Not only is crawfish bait expensive, it makes for additional labor considerations and involves the task of handling bait which is messy and which often has a strong unpleasant odor. The use of bait for the purpose of harvesting crawfish although a primitive and expensive procedure has yet to be replaced by alternative methods.
Recognized as a bottle neck in the culture of crawfish, much research by universities and many individuals has been conducted towards finding an improved method and design for harvesting crawfish.
Some of the alternate approaches to the traditional "baited" trap includes (1) electric harvesters which "shock" crawfish to the surface and allows a scooping device to catch them as a harvester moves through a pond; (2) the use of water current which takes advantage of behavorial tendencies for crawfish to move in certain patterns according to direction of flow; (3) traditional and modified seines and trawls; (4) the use of vibrations to attract or repel crawfish; and finally (5) chemical attractants.
Additional research has been conducted to improve traditional "baited" trap use and design. Research for improving the efficiency of baited traps have included the development of an irrigation type harvester which moves slowly back and forth across a pond setting and emptying traps as it goes.
The research and development of artificial (processed) bait has become influential and widely used among crawfish farmers although natural bait such as cut fish continues to be used in large quantities.
The disadvantage of using bait to entice crawfish into a trap extends far beyond the cost of the bait itself. Bait which is subject to spoilage must be refrigerated. On a daily basis harvesting requires bait such a fish to be cut into individual portions suitable for each trap, placed in each trap and then removed when it is no longer fresh. Often bait, both natural and artificial, becomes mixed with crawfish when traps are being emptied. Old bait mixed in with live crawfish increases mortality and spoilage, appears unappetizing and must be removed before cooking or processing.
Two essential criteria must be met before a baitless method of harvesting crawfish can be considered successful.
The method must first have the ability to catch sufficient numbers of marketable crawfish within a specified body of water. Secondly, the method and devise must be cost effective to both construct and use. Other factors to be considered include the ability for a baitless trap or method of harvesting to catch larger crawfish while allowing smaller crawfish to remain in the ponds for continued growth. Such a method should also be adaptable for use in a significant portion of commercial crawfish habitant during the harvest season.
In addition to being attracted to bait, it is well known that crawfish exhibit a behavorial characteristic for seeking out places to hide. As typical for most nocturnal creatures crawfish are active at night moving about from place to place seeking food and optimum environmental conditions including shelter. During daylight hours, crawfish are relatively inactive frequently remaining in or near a place to hide. Often crawfish maintain burrows on the edges or bottoms of ponds as a source of shelter in which they can hide and escape from their many predators. In natural habitats like swamps, streams and other natural bodies of water, natural debris such as rocks, tree limbs and roots, as well as man-made substrates is often are available for crawfish to hide in and among.
Cultivated crawfish ponds especially those planted with rice are usually free of an abundance of substrate other than the rice, stable itself. Under such conditions the proper use of artificial hides provides a strong attractant for crawfish. Crawfish will move in and out through appropriately shaped hides when active, although this behavior is not as apparent during daylight hours.
In order to take advantage of this behavorial characteristic, a viable trapping device using hide(s) as an attractant, would have to catch sufficient numbers of crawfish in order to considered a successful harvesting technique. It has been falsely assumed that as a method of harvesting crawfish, the use of hides could not function effectively. This assumption is based on the observation that once a crawfish "inhabits" a hide it often remains there for long periods of time during which it discourages other crawfish from using the same space. If a crawfish were therefore to remain within one particular hide, it would require numerous hides to attract sufficient quantities of crawfish. Large numbers of such hides would be expensive, excessively bulky and unmanageable to harvest as they would be awkward to lift from the water and would create problems with removing the crawfish from the hide(s) as it is common for crawfish to resist being "dislodged" from within the protection of the hide.
During the research of the present invention it was discovered that one or a few relative individual tubes could be as effective as many individual hides if individual crawfish entered but did not remain within the inner space of the tube. The extent to which this "baitless" trap becomes efficient depends on a variety of factors but to a very large extent it depends on whether or not the tube or hide remains occupied or vacant.
The design of the present invention is such that once a crawfish enters the tube and passes beyond a trap door he will discover the only path of movement is through the tube away from the direction of entrance and towards a point of collection. For the efficiency of the trap design a second trap door is positioned near the exit of the tube which opens into a collection chamber. The second trap door functions to keep crawfish from reentering the tube from the collection chamber side and thus prevents interference with additional crawfish moving through the trapping tube towards the collection chamber. In this fashion the entrance to the trap remains, for the most part, available for occupancy. The result of this design therefore minimizes the number of trapping tubes necessary for use thus reducing construction cost and making for a trap which is practical to lift and empty. The movable door(s) which conforms to the inside dimensions of the tube are made out of a strong but lightweight material such as plastic. Trap door(s) at the entrance of the trapping tube(s) are positioned in such a way as to provide a perceptible space which the crawfish would occupy. The trap door(s) used in the present invention can be made of either sinking or floating material.
If a floating door is used, the end of the door most proximal to the entrance is attached by a simple hinge, such as an O ring made of plastic or metal, to the bottom or floor of the tube so that the most distal end will float to the roof or top of the tube. As a crawfish enters the openings of the tube, he will position himself on top of the trap door discovering that his weight and his movement into the tube will move the floating door downward creating an opening for access further into the tube. Once a crawfish moves beyond the length of the trap door, the distal end of the trap door will again float to the top of the tube and thus seal off the passage way. When a crawfish, which has moved beyond the trap door tries to move back towards the entrance, the angle of the trap door would then be such that his movement only causes the unattached end of the door to be more firmly forced against the top of the tube. With this restriction, a crawfish would then become limited to movement towards the collection chamber.
If a sinking trap door is used near the entrance of the tube trap, the end of the door proximal to the entrance is attached to the top of the tube with the distal end of the trap door sinking at an angle and resting on the bottom of the tube. The sinking trap door works similar to the floating door with the exception of having movement which is directionally opposite. In the case of the sinking trap door a crawfish forces the door upward moving under it as he progresses deeper into the tube. With the effort to move back towards the entrance of the trap, the crawfish walks on top of the trap door which is being held to the top of the tube by a hinge on one end and is being forced against the floor of the tube on the other end. Again this creates a situation in which a crawfish is limited in movement toward the direction of the collection chamber.
A second trap door near the exit of the tube and at the entrance of the collection chamber functions for the overall improvements of the trap design to prevent crawfish which are already in the collection chamber from re-entering the trapping tube and occupying the tube space behind the first trap door. Such a second trap door working by either the floating or the sinking method similar to that first trap door is positioned so as not to create an unnecessary space on the collection chamber side of the tube which a crawfish could occupy. This can be accomplished by beveling the tube and/or positioning the trap door so that when observed from the collection chamber side, the tube would not appear to have a recess large enough to accommodate a harvestible size crawfish.
Thus, a second trap door prevents crawfish from returning to the space behind the first trap door and the positioning of a second trap door in conjunction with contour of the tube exit eliminates unnecessary space from the tube behind the second door.
For the improved efficiency of the overall trap design trap doors can be constructed so as to allow both a perception to the crawfish that space behind the door is available and that the weight or resistance of the trap door does not present an obstacle for utilizing this space. Trap doors should therefore be constructed with a minimal thickness and shape so as up and down movement will not be restricted by the sides of the tube while at the same time providing sufficient width to block off the passage way when the door is in a closed position. Slits or holes in the trap door increases the perception of available space behind the door and allows water to flow through the door reducing resistance and making access into the tube easier by the crawfish. The weight or buoyancy of a trap door should, however, be sufficient so that the door will sink or float closed in a definitive manner and not remain open except for the short time it takes for the crawfish to pass through.
The collection chamber of the tube trap should correspond in size to be no larger than necessary to accommodate the expected maximum yield for each trap. Similar to traditional wire crawfish traps using bait at least a portion of the collection chamber should be constructed out of a graded mesh material sized to retain larger crawfish while permitting smaller ones to escape. The collection chamber can be contoured in relation to the tube to improve the efficiency at the trap in such a way so that when crawfish accumulate in the chamber they do not interfere with crawfish in the tube(s) attempting to enter the collection chamber. One way to accomplish this it to have the exit end of the tube bent or slanted upwards away from the bottom of the trap thus allowing crawfish to enter a tube which is at or near the bottom of the pond and exit the tube inside the trap above the floor of the collection chamber. In this fashion, crawfish collect mostly down along the bottom of the trap away from the tube exit.
Other considerations for the efficiency of this baitless trap design includes the positioning of the trap door(s) and the shape of the entrance of the tube. It was found that the positioning of the entrance trap door was important to the willingness of the crawfish to enter the trap. Trap doors at the entrance of the trap which were not recessed enough were slower to attract crawfish than those which were sufficiently recessed. If the trap door was recessed too far into the tube, crawfish would occupy the space in front of the trap door and would be slower to move deeper into the tube. Trap door(s) recessed too far into the tube would also make for additional cost as the tube would be longer than necessary.
Additional factors though subtle in their individual effect make for improved efficiency in the overall trap design. One such modification concerns the shape and size of the entrance opening. The entrance end of a tube was found to attract crawfish faster if the opening surface area was increased giving crawfish more opportunity to discover the way into the trap. Experimentation demonstrated that beveling the tube(s) and/or flaring them outward near the entrance provided crawfish with a greater ability to discover access within the tube(s). In this fashion crawfish approaching the trap from either side could more easily perceive the entrance opening in addition to those approaching the trap from a head-on direction.
Another factor in influencing the efficiency of a tube trap is the length of space between the first trap door and the exit opening or a second trap door. Crawfish passing through the first trap door were less likely to continue forward progress if they encountered a second trap door before their body had completely passed beyond the first door. If the space between the trap door(s) or the first trap door and exit opening is excessively long, it increases the time it takes for the crawfish to enter the collection chamber, makes the trap more cumbersome and makes for unnecessary cost of additional construction materials.
Although tube traps are designed to have a baitless feature as an attractant for a method of harvesting crawfish, under certain circumstances, bait may be added to these traps which in such a case would function to provide both a baitless attractant and a baited attractant.
The use of a baitless attractant as a feature on this trap design is, therefore, not intended to function necessarily to the exclusion of bait but under certain conditions, may include the use of bait as an attractant in addition to this baitless feature.
It should also be noted that when using bait as an attractant with the trapping tubes of this invention clear or transparent tubes may be employed for use and although not preferred because it minimizes the baitless aspect they could be used to function according to its trapping aspect or features.
By using a trap which has a baitless attractant, a mechanical lifting and emptying devise becomes much more practical. Without having to use bait a mechanical arm attached to a harvester (boat, etc.), could lift each trap, invert it so that the crawfish will fall out an escape proof opening in the collection chamber and onto a conveyor or trough leading back to the harvester, and then reset the trap back into the water. As a labor saving device, the trap and the mechanical arm would conform to each other and function in a motion which allows continuous and sustained movement of a harvester moving throughout a crawfish pond.